The present invention relates to adjustable instruments for use with a localizing device. More particularly, certain embodiments of the present invention relate to an adjustable drill guide and an adjustable fixator for use with an electromagnetic localizing system during surgery.
During surgical operations, it is beneficial to be able to track the direction and progress of a surgical instrument, such as a drill bit, into a patient's body in order to ensure that the instrument is directed into the appropriate point in the body. Therefore, surgical tracking systems have been developed that are able to display and monitor movement of a surgical instrument relative to an image of the patient's body.
One system used for surgical tracking is an electromagnetic tracking system. In a typical electromagnetic tracking system, the area of the patient's body where surgery is to take place is imaged using an imaging technology such as an MRI, X-ray, CT scan or any other appropriate imaging method. The scanned images are stored in a computer system and are displayed on a screen during the surgical procedure. Localizing devices are then used to track the movement of surgical instruments relative to the patient's body. For example, a transmitter that emits an electromagnetic field is secured to the patient's body proximate the area of the patient's body where surgery is to take place. Typically, the transmitter is secured to a fixator that is fixedly attached to the patient's bone by bone screws. The instrument that is to be tracked during surgery has a receiver mounted thereto that receives the electromagnetic signals from the transmitter. The transmitter and receiver are both connected to the computer that displays the image. The computer translates the location of the transmitter on the patient's body to an equivalent point on the image. Then, by monitoring the signals sent from the transmitter to the receiver as the instrument is used in surgery, the computer is able to track the movement of the instrument relative to the transmitter and transpose the movement to the image. Therefore, medical personnel may closely track the positioning and progress of the instrument at the patient's body during surgery by examining the image.
Alternatively, in some electromagnetic systems, a receiver is placed on the patient and the instrument, and a field transmitter is placed proximate the patient. The receivers and transmitter are connected to the computer, and the computer is then able to track the movements of the instrument on an image similarly to the system using just a single receiver.
However, the conventional electromagnetic tracking systems suffer from some drawbacks. The transmitter and receiver are restricted in the distances that they may be situated apart and the positions in which they may be oriented towards each other. For example, the transmitter and receiver may not effectively communicate when they are situated within a few inches of each other. Conversely, the electromagnetic field created by the transmitter may not reach the receiver if the transmitter and receiver are situated more than about 18 inches from each other. Additionally, the presence of any devices that generate their own electromagnetic fields, such as an electric surgical drill, proximate the tracking system may interfere with the electromagnetic communication between the transmitter and the receiver. Likewise, the presence of some metal objects, such as retractors or operating tables, proximate the tracking system may interfere with the electromagnetic communication between the transmitter and the receiver. The interference is especially pronounced when a metal object is located between the transmitter and receiver. The effect of this interference may be a loss of ability to track with the system or a decrease in the accuracy of the tracking. An operator can avoid the difficulties associated with the orientations of the localizers and the distances between the localizers by carefully placing the localizers relative to one another such that any interference is minimized. However, because the fixator is securely fastened into the patient's bone by screws and the receiver is securely mounted to the instrument, and the instrument must typically be in a specific position to perform the intended surgical task, it can be difficult for an operator to adjust the localizers relative to each other in order to achieve effective electromagnetic communication. Therefore, there is a risk during surgery of a surgeon being unable to track the surgical instrument should an interfering object come near the localizers or should the instrument become positioned too far away from, or too close to, the fixator.
Therefore, a need exists for an improved method of positioning the localizers on an instrument and a fixator in order that the localizers can communicate during a surgical procedure.